Controlled electrode for field emission discharge devices



Sept. 24, 1946.- J. H FINDLAY ErAL 2,407,979

CONTROLLED ELECTRODE FOR FIELD EMISSION DISCHARGE DEVICES Filed Sept.26, 1942 Www ATTORNEY Patented Sept. 24, 1946 UNITED STATES PATENTOFFICE CONTROLLED ELECTRODE FOR FIELD EMISSION DISCHARGE DEVICESPennsylvania Application September 26, 1942, Serial No. 459,776

7 Claims. 1

The present invention relates to discharge devices and more particularlyto such devices wherein operation is initiated by a field emission areas an electron source, and constitutes an improvement n the structuresuch as shown in the copending applications of Charles M. Slack et al.,Ser. No. 412,566, filed Sept. 27, 1941, and. Ser. No. 459,775, filedconcurrently herewith, both of which are assigned to the same assigneeas the present invention.

In the operation of devices of this character and as pointed out more indetail in the above noted application, Ser. No. 412,566, field emissionof electrons occurs between a pair of cold electrodes due to the highpotential gradient at the cathode. This electrostatic field pullselectrons from one of the electrodes, which causes a minute aredischarge to form between the starting electrode and the cathode,apparently due to evolved metallic particles, and the positive ionbombardment caused by ionization of the evolved metal vapor resultingfrom the are forms a cathode spot which reduces the impedance of thedevice, and an electron discharge between the cathode and anode of thedevice almost instantaneously occurs following initiation of the arcdischarge between the starting electrode and cathode.

In a device of this character it inherently follows that a certainamount of material will be lost from and transferred between the closelyspaced electrodes between which the field emission arc is initiated.This is because operation of a field emission arc discharge device doesnot depend upon the ionization of volume gases or vapors within thedevice, but is dependent rimarily on positive ions which are the resultof the vaporized material from one of the elec-- trodes interacting withthe field emission electrons. lT'he positive ions are necessary torelieve space charge and to increase the field concentration at thcathode spot which in turn produces more field and Schotky electrons.Inasmuch as a voltage of sufficient magnitude, depending upon theinitial spacing of the starting electrode and cathode, is required toinitiate the field emission are discharge, there is a tendency for suchvoltage to increase as the electrodes wear away during operation of thedevice.

In the above noted copending application Ser. No. 459,775 filedconcurrently herewith, a structure is shown and claimed for maintainingthe electrode spacing constant during the life of such device whichinherently maintains the voltage required to initiate the field emissionare discharge substantially constant, and whenever such voltage tends tovary such is an indication that the electrode spacing needs readjustingto maintain this constancy of spacing and initiating voltage. Thestructure as shown in such copending application depends primarily forits operation upon the flow of electrical current through a bimetallicelement and therefore might be said to be electrically controlled.

It is the primary object of the present invention to provide a dischargedevice wherein operation is initiated by a field emission arc and thespacing between the electrodes which support such are discharge ismechanically controlled so as to maintain the electrode spacingconstant.

Another object of the present invention is the provision of a dischargedevice wherein operation is initiated by a field emission are dischargeand in which movement of the ignition electrodes is mechanicallycontrolled exteriorly of the device at will by an operator to compensatefor the inherent tendency for the electrode spacing to increase due toloss of material during operation.

A further object of the present invention is the provision of adischarge device wherein operation is initiated by a field emission aredischarge between a pair of ignition electrodes and in which the voltagerequired to initiate the field emission are is maintained substantiallyconstant despite an inherent tendency for the spacing between theelectrodes to increase due to loss of electrode material by mechanicallyadjusting the electrode spacing ex-teriorly of the device at the will ofan operator.

Still further objects of the present invention will become obvious tothose skilled in the art by reference to the accompanying drawingwherem:

Fig. 1 is a sectional view in elevation of a device constructed inaccordance with the present invention wherein operation is initiated bya field emission are discharge showing a mechanical control of thespacing between the electrodes as well as a schematic diagram of anoperating circuit.

Fig; 2 is a sectional view taken on the lines IIII of Fig. 1 and lookingin the direction indicated by the arrows, and

Fig. 3 is a sectional view taken on the lines I1'IIII of Fig. 1 andlooking in the direction indicated by the arrows.

Referring now to the drawing in detail, the discharge device 4 as shownin Fig. 1 comprises an envelope 5 of vitreous material provided with apair of electrodes 6 and l which are of substantially rectangularconfiguration and of uniform cross section disposed parallel to eachother and having their edges spaced apart a minute distance of less thanapproximately .010 inch, depending upon the voltage to be applied. Theseelectrodes 6 and I are formed of suitable metal such as copper, gold,silver, uranium, or the like, and welded or otherwise secured toleading-in and supporting conductors 8 and 9. The leadingin andsupporting conductor 8 is Welded, soldered, or otherwise ainxed to aflexible metallic diaphragm H] of copper or the like, which latter atits peripheral edge I2 forms an hermetic seal with the vitreous envelope5; and exteriorly of the device 4 such leading-in and supportingconductor is provided with a metallic terminal I3 of copper, tantalum,molybdenum, or the like, welded or otherwise rigidly afiixed theretowhich thus constitutes an integral part of the leadingin and supportingconductor 8. The leading-in and supporting conductor 9 is similarlysecured to a metallic terminal M of copper, tantalum, molybdenum or thelike, which thus forms an integral part thereof and, as shown, suchterminal is provided with an enlarged diameter portion having a featheredge l5 also forming an hermetic seal with the vitreous envelope 5. Bothof the leading-in and supporting conductors are provided with suitablebaflies I5 for the purpose of preventing hot metallic particles from theelectrodes 6 and I from falling in the vicinity of the seals and thusdestroying the same.

An anode ll of a refractory metal such as tungsten, molybdenum, or thelike, and of substantially U-shape, is also supported by a leading-inconductor l8 so as to position the anode a short distance from theelectrodes 6 and l and overlapping th gap between these latterelectrodes. This leading-in and supporting conductor 18 is secured to aterminal H) which is identical to and forms an hermetic seal with theenvelope 5 in the same manner as previously mentioned with respect tothe terminal l4. After assembly of the device it is exhausted to a highdegree of evacuation through an exhaust tip 20 with the various metallicparts being thoroughly degasified, as is customary in the art, so thatsatisfactory operation is entirely independent of vapor or gas presentin the device.

If desired, however, a metal vapor such as mercury may be introducedinto the envelope 5 prior to tipping off at 20, which also results insatisfactory operation so long as its pressure is such that the spacingbetween the ignition electrodes is less (and preferably many times less)than the mean free path of electrons in the vapor so that ignition andoperation of the device is entirely independent of the mercury vaporpresent.

In the embodiment as shown in Fig. 1 the electrode 6 constitutes thestarting electrode, while the electrode 7 is the cathode. For thepurpose of initiating a field emission arc between these two electrodes,a suitable source of energy is provided such, for example, as a hightension transformer 22, the secondary winding 23 of which has one endconnected to the terminal I3 and hence to the starting electrode 6through the leading-in conductor 8, while the remaining end is groundedat 24. Since the terminal 14 is also grounded at 25, a circuit from thesecondary winding 20 to the cathode l is completed through th leading-inand supporting conductor 9. In order to energize the transformer 22, theprimary winding 26 thereof is connected to a suitable source of supplysuch, for example, as shown more in detail in the above noted copendingapplication, Ser. No. 459,775, so that when the primary winding 26 isperiodically energized, an appropriate ignition voltage is impressedacross the electrodes 6 and 1. However, since the circuit per se formsno part of the present invention, further detailed description isbelieved superfiuous.

Although the discharge device 4 as shown can be employed for numerouspurposes and circuits, it is illustrated as a control device forcontrolling the supply of energy to a load. As a typical purpose, it isshown in Fig. 1 as a control tube for a high voltage circuit and forsuch application one. end of the secondary winding 21 of a high tensiontransformer 28 is grounded at 25; and since the cathode is also groundedat 25, as above mentioned, a connection is thus completed to the cathode1 through the leading-in and supporting conductor 9. The remaining endof the secondary winding 21 connects to load as indicated by suchlegend, as does the anode I! through the leading-in and supportingconductor l8 and terminal M. The primary winding 29 of the transformer23 may be connected to a suitable source of the customary domesticpotential of -230 volts. When an impulse of electrical energy passesthrough the primary winding 26 of the transformer 22, a high voltageimpulse is induced in the secondary Winding 23 of this transformer 22which voltage is impressed across the starting electrode 6 and cathodeI. Since these electrodes are closely spaced, as above noted, a highpotential gradient results which initiates a field emission arcdischarge therebetween. The space charge, and consequently the impedanceof the device, is accordingly reduced and an electron discharge almostinstantaneously occurs between the cathode l and th anode I! ashereinbefore mentioned, which enables the load to be energized from thetransformer 28.

As previously mentioned herein and as set forth in the concurrentlyfiled copending application, Ser. No. 459,775, there is a gradualwearing away of the ignition electrodes and particularly the startingelectrode 6. Moreover, the electrode spacing between the startingelectrode 6 and cathode I, even though it might not be measureddirectly, is nevertheless a function of the voltage required to initiatethe field emission arc discharge. Consequently, this wearing away of theelectrodes causes an increase in the voltage required to initiate thearc, as above mentioned, which not only affects the characteristics ofthe device, but considerably shortens its useful life. Yet by knowingthe relationship of voltage and electrode spacing, which naturallyvaries with different materials and electrode configurations, and byholding the spacing constant, the voltage will likewise be maintainedconstant, for any tendency of voltage variation is an indication that anadjustment of the electrode spacing is required in order to maintainconstancy of ignition voltage.

In accordance with the present invention, a constant voltage is obtainedby a mechanical structure for effecting controlled movement oradjustment of the electrode spacing. Such structure, as illustrated inFig. 1, comprises a base member 30 of suitable insulating material towhich a block 32 is secured, such as by means of a screw 33. The block32 is provided with arecess engageable by the metallic terminal [4 of rthe device. A further block 34 is arranged to slide between a pair ofguides 35 upon the upper surface of the base til. For the purpose ofmoving the block 34-, the base 35! is provided with 2. lug 36 threadedlyengaged by an adjustment screw 31 having a knurled handle 33 andprovided with a collar 39 fitting into a recess provided in a retainerplate All. The block 3 3, similar to the block 32, is provided with arecess which is engaged by the metallic terminal 13 forming an integralpart of the leading-in and supporting conductor 8.

During operation of the device as above noted, when the electrodes 6 andI wear away to the point where there is a tendency for the ignitionvoltage to vary, it is only necessary for an operator to rotate theknurled handle 33 of the adjusting screw 37 in a counter-clockwisedirection, and since the adjusting screw threadedly engages the lug 36and loosely engages the block 3 5, the latter will be slid along thebase 30 to the left, as shown in Fig. 1. Inasmuch as the metallicterminal 13 forming an integral part of the leading-in and supportingconductor 8 fits into the block as, the leading-in and supportingconductor 8, together with the starting electrode 6 supported thereby,will be moved due to the flexible metallic diaphragm Ii! whichaccordingly prevents a strain being placed upon the hermetic seal wherethe leading-in and supporting conductor passes through the wall of thedevice. lihis movement of the adjusting screw 31 will accordingly causethe electrode 6 to be moved in closer proximity to the cathode l, thusagain setting such spacing to that desired and main taining the spacingtogether with the ignition voltage substantially constant.

It should also be noted that although the leading-in and supportingconductor 8 has been shown as secured to the flexible diaphragm iii,such is not absolutely essential, but, on the other hand, the hermeticseal formed between the leading-in and supporting conductor 8 and theenvelope 5 may be identical to that of the leading-in and supportingconductor 9. In other words, the leading-in and supporting conductor 8may be provided with a terminal member I4 and movement of the leading-inand supporting conductor still obtained by regulation of the adjustingscrew 31. This is because appreciable flexibility results even with theprovision of a metallic terminal, such as shown at l4, allowing movementof the leading-in conductor without placing undue strain on the seal,particularly since the adjustment of the spacing between the electrodes6 and l at any time is exceptionally minute, being of the order of .010inch as above noted. However, in some instances it may be preferable toemploy a flexible metallic diaphragm such as shown at ll) in Fig. 1.

From the foregoing description it thus becomes obvious to those skilledin the art that an electron discharge device wherein operation isinitiated by a field emission are discharge is herein provided in whichthe spacing between the electrodes, and hence the voltage required toinitiate such discharge, is maintained substantially constant. Moreover,such constancy is obtained at the will of an operator by simpleadjustment of a mechanical member disposed exteriorly of the devicewhich upon operation causes controlled movement of the leading-in andsupporting conductor for one of the electrodes, together with theelectrode carried thereby, so that a fixed spacing is maintained betweenthe ignition electrodes, thus compensating for their wearing away due toevolution of metallic particles caused by the field emission arcdischarge.

lthough one embodiment of the present invention has been shown anddescribed, it is to be understood that other modifications may be madewithout departing from the spirit and scope of the appended claims.

We claim:

1. A discharge device whe'ein operation is initiated by field emissionof electrons comprising a pair of oppositely disposed spaced electrodesbetween which a field emission are discharge occurs upon the applicationof a potential thereto and subject to deterioration tending to increasethe gap therebetween during operation, an anode in juxtaposition to saidpair of electrodes for supporting an electron discharge with one of theelectrodes of said pair immediately following the field emission aredischarge between said pair of electrodes, and means disposed exteriorlyor" said device and operable by an operator at will to cause relativemovement between said pair of electrodes to maintain the spacingtherebetween substantially constant during the useful life of saiddevice.

2. A discharge device wherein operation is initiated by field emissionof electrons comprising a pair of oppositely disposed spaced electrodesbetween which a field emission are discharge occurs upon the applicationof a potential thereto and subject to deterioration tending to increasethe gap therebetween and the voltage required to ini tiate the fieldemission arc discharge during operation said device, an anode positionedadjacent said pair of electrodes for supporting an electron dischargewith one of the electrodes of said pair immediately following the fieldemission are discharge between said pair of electrodes, and meansdisposed exteriorly of said device and operable at will by an operatorto maintain the voltage required to initiate the field emission aredischarge constant despite deterioration of said pair of electrodesduring the useful life of said device.

3. A discharge device wherein operation is ini tiated by field emissionof electrons comprising a pair of oppositely disposed spaced electrodesbetween which a field emission arc discharge occurs upon the applicationof a potential thereto and subject to deterioration tending to increasethe gap therebetween during operation, an anode positioned adjacent saidpair of electrodes for supporting an electron discharge with one of theelectrodes of said pair immediately following the field emission arcdischarge between said pair of electrodes, and a mechanical memberdisposed exteriorly of said device and operable at will by an operatorto cause relative movement between said pair of electrodes to maintainthe spacing therebetween substantially constant despite deterioration ofsaid pair of electrodes during the useful life of said device.

4. A discharge device wherein operation is initiated by field emissionof electrons comprising a sealed envelope. a pair of oppositely disposedspaced electrodes in said envelope between which a field emission aredischarge occurs upon the application of a potential thereto and subjectto deterioration tending to increase the gap therebetwcen and thevoltage required to initiate the field emission arc discharge duringoperation of said device, a leading-iii and supporting conductor foreach electrode of said pair and forming an hermetic seal with saidenvelope, an anode positioned adjacent said pair of electrodes forsupporting an electron discharge with one of the electrodes of said pairimmediately following the field. emission are discharge between saidpair of electrodes, and a member disposed exteriorly of said envelopeand operable at will by an operator to cause movement of one of saidleading-in and supporting conductors together with the electrodesupported thereby for the purpose of maintaining the spacing betweensaid pair of electrodes substantially constant despite deterioration ofthe latter during the useful life of said device.

5. A discharge device wherein operation is initiated by field emissionof electrons comprising a sealed envelope, a pair of oppositely disposedspaced electrodes in said envelope between which a field emission aredischarge occurs upon the application of a potential thereto and subjectto deterioration tending to increase the gap therebetween and thevoltage required to initiate the field emission arc discharge duringoperation of said device, a leading-in and supporting conductor for eachelectrode of said pair and forming an hermetic seal with said envelope,an anode positioned adjacent said pair of electrodes for supporting anelectron discharge with one of the electrode of said pair immediatelyfollowing the field emission arc discharge between said pair ofelectrodes, and a mechanical member engageable with the leading-in andsupporting conductor for one of the electrodes of said pair exteriorlyof said envelope and operable at will by an operator to apply a tensionto said conductor to cause deflection thereof with attendant movement ofthe electrode supported thereby for the purpose of maintaining thespacing between said pair of electrodes substantially constant despitedeterioration of the latter during the useful life of said device.

6. A discharge device wherein operation is initiated by field emissionof electrons comprising a sealed envelope, a pair of oppositely disposedspaced electrodes in said envelope between which a field emission aredischarge occurs upon the application of a potential thereto and subjectto deterioration tending to increase the gap therebetween and thevoltage required to initiate the field emission are discharge duringoperation of said device, a leading-in and supporting conductor for eachelectrode of said pair, a resilient hermetic seal between one of saidleading-in and supporting conductors and said envelope, an anodepositioned adjacent said pair of electrodes for supporting an electrondischarge with one of the electrodes of said pair immediately followingthe field emission are discharge between said pair of electrodes, and amember disposed exteriorly of said envelope and engageable with theleadingin and supporting conductor for one electrode of said pair andoperable at will by an operator to cause movement of said conductor atthe resilient seal with said envelope accompanied by movement of theelectrode supported thereby for the purpose of maintaining the spacingbetween said pair of electrodes substantially constant despitedeterioration of the latter during the useful life of said device.

'7. A discharge device wherein operation is initiated by field emissionof electrons comprising a sealed envelope, a pair of oppositely disposedspaced electrodes in said envelope between which a field emission aredischarge occurs upon the application of a potential thereto and subjectto deterioration tending to increase the gap therebetween and thevoltage required to initiate the field emission are discharge duringoperation of said device, a leading-in and supporting conductor for eachelectrode of said pair, a flexible metallic diaphragm secured to one ofsaid leading-in and supporting conductors and forming an hermetic sealwith said envelope, an anode positioned adjacent said pair of electrodesfor supporting an electron discharge with one of the electrodes of saidpair immediately following the field emission are discharge between saidpair of electrodes, and a member disposed exteriorly of said envelopeand engageable with the leading-in and supporting conductor for oneelectrode of said pair and operable at will by an operator to causeflexing of said diaphragm and attendant movement of one of saidleading-in conductors together with the electrode carried thereby forthe purpose of maintaining the spacing between said pair of electrodessubstantially constant despite deterioration of the latter during theuseful life of said device.

JOHN H. FINDLAY. CLARENCE E. DAWLEY. ANDREW PFEIFFER.

